There are essentially two types of dyeing.
The first is semi-permanent dyeing or direct dyeing, which involves dyes capable of giving the hair's natural colour a more or less pronounced change.
The dyes used are coloured and colouring substances that have a certain affinity for keratin fibres.
It should be noted that this type of dyeing fades out after several washes, which may be an inconvenience.
When it is desired to obtain a coloration that is lighter than the original colour of the fibres, it is necessary to use, with the direct dyes, at least one oxidizing agent, under alkaline pH conditions.
However, these conditions of use are not free of consequences on the properties of the treated fibres. Specifically, in the long run, the fibres are more or less degraded and have a tendency to become coarse, dull, brittle and difficult to style.
The second is permanent dyeing or oxidation dyeing. This is performed with oxidation dye precursors, which are colourless or weakly coloured compounds, comprising at least one oxidation base optionally combined with one or more couplers. Once mixed with oxidizing products, at the time of use, the precursors may give rise to coloured compounds and dyes via a process of oxidative condensation.
Given the necessary presence of an oxidizing agent in this type of dyeing, the drawbacks mentioned above also occur in this case.
It has recently been found that compositions comprising at least one fluorescent compound represent an advantageous alternative to standard processes using an oxidizing agent. Thus, for dark hair, more particularly hair with a tone height of less than or equal to 6 (dark blond), preferably less than or equal to 4 (chestnut-brown), it can be seen that there are regions for which the curve of reflectance as a function of the wavelength (between 500 and 700 nm) of hair treated with the composition comprising the fluorescent compound is higher than the curve corresponding to untreated hair. Consequently, the hair appears lighter, without it being necessary to use an oxidizing agent.
It is recalled that the notion of “tone” is based on the classification of the natural shades, one tone separating each shade from the shade immediately following or preceding it. This definition and the classification of the natural shades are well known to hairstyling professionals and are published in the book “Sciences des traitements capillaires [Hair treatment sciences]” by Charles Zviak, 1988, published by Masson, pp. 215 and 278. The tone heights range from 1 (black) to 10 (light light blond), one unit corresponding to one tone; the higher the figure, the lighter the shade.
Although such compositions constitute an advance in this field, it nevertheless remains that the stability on storage of these compositions has room for improvement.
Moreover, it would also be advantageous to further increase the wash-fastness and shampoo-fastness of the colorations obtained using these compositions.